Sound emissions of an automotive engine cooling system are studied using both single-microphone directivity measurements and a rotating beamforming technique. These measurements provide reference acoustic data on such a system and some new understanding of the effect that the radiator induces on the distribution of sound sources. Indeed, the beamforming results indicate that, above the frequency limit allowed by the Rayleigh criterion, it is possible to localize and quantify the noise sources even through the heat-exchanger core. Moreover, for the investigated operating points along the fan performance curve, the sources are always distributed at the tip of the blades and, in particular, at the leading edge. The present evidence, confirmed by the similar trends of the frequency spectra with and without the heat exchanger, leads to the conclusion that the dominant sound mechanism is the turbulence-interaction noise. Nevertheless, this turbulence is produced within the gap between the fan ring and its casing rather than generated by the radiator core. The latter appears to induce negligible acoustic transmission losses but, more significantly, is found to have a minimal influence on the aerodynamic modification of sound sources for all the analyzed operating conditions.

An automotive cooling module working at three different operating conditions is investigated using a microphone array method. Experiments on an open rotor and on a full module configurations were conducted in the ALCOVES anechoic chamber of the von Karman Institute for Fluid Dynamics, Belgium. The acoustic data are post-processed using the ROtating Source Identifier algorithm. As first step, the method was applied for the fan-alone configuration at the nominal operating point. The sound maps of one-third octave band are discussed with respect to the minimum resolving frequency emerging by the Rayleigh criterion. Integrated spectra of the whole beamforming maps are used to validate the method whereas acoustic characteristics of the fan are identified by evaluating integrated spectra of each blade separately. Subsequently, the ROSI method was applied to both configurations, demonstrating the acoustic transparency of the automotive heat exchanger. Depending on the adjusted mass flow rate, sound sources are located on the leading or trailing edges of the fan blades. To complement the analysis, sound directivity measurements have been carried out in the anechoic wind tunnel at the University of Sherbrooke, Canada, on an another sample of the same engine cooling module.